Heritability and genetic integration of tooth size in the South Carolina Gullah

Objectives: This article provides estimates of narrow-sense heritability and genetic pleiotropy for mesiodistal tooth dimensions for a sample of 20th century African American individuals. Results inform biological distance analysis and offer insights into patterns of integration in the human dentition. Materials and Methods: Maximum mesiodistal crown dimensions were measured using Hillson-FitzGerald calipers on 469 stone dental casts from the Menegaz-Bock Collection. Narrow-sense heritability estimates and genetic and phenotypic correlations were estimated using SOLAR 8.1.1 with covariate screening for age, sex, age*sex interaction, and birth year. Results: Heritability estimates were moderate (∼0.10 – 0.90; h² mean = 0.51) for most measured variables with sex as the only significant covariate. Patterns of genetic correlation indicate strong integration across tooth classes, except molars. Comparison of these results to previously published work suggests lower overall heritability relative to other human populations and much stronger genetic integration across tooth classes than obtained from nonhuman primate genetic pleiotropy estimates. Conclusions: These results suggest that the high heritabilities previously published may reflect overestimates inherent in previous study designs; as such the standard estimate of 0.55 used in biodistance analyses may not be appropriate. For the Gullah, isolation and endogamy coupled with elevated levels of physiological and economic stress may suppress narrow-sense heritability estimates. Pleiotropy analyses suggest a more highly integrated dentition in humans than in other mammals.